ROCKVILLE, Maryland, June 22, 2026
REGENXBIO has announced a significant regulatory milestone for NAVSUNLI™ (clemidsogene lanparvovec-sngl, RGX-121), its investigational gene therapy for Mucopolysaccharidosis Type II (MPS II), also known as Hunter syndrome. Following extensive discussions with the U.S. Food and Drug Administration (FDA), the company confirmed alignment on a pathway toward accelerated approval, potentially positioning NAVSUNLI as the first approved gene therapy and first one-time treatment for MPS II. Importantly, the FDA indicated that no additional clinical studies or patient enrollment will be required, allowing the agency to evaluate existing long-term biomarker and clinical data from the ongoing CAMPSIITE® study. REGENXBIO expects to hold a Type A meeting with the FDA in July 2026 and plans to rapidly resubmit its Biologics License Application (BLA) during the third quarter of 2026. The announcement marks a major advancement for patients and families affected by Hunter syndrome, a devastating ultra-rare neurodegenerative disorder with significant unmet medical needs.
FDA Supports Accelerated Approval Pathway for NAVSUNLI
The latest regulatory update follows REGENXBIO’s appeal of the Complete Response Letter (CRL) received in February 2026. During recent discussions, FDA officials acknowledged that the existing clinical evidence supporting NAVSUNLI is sufficient for consideration under the accelerated approval framework. Notably, the agency withdrew its previous recommendation requiring an untreated control arm and confirmed that additional studies are not necessary prior to review. Instead, the FDA will assess the extensive long-term clinical and biomarker data already generated in the CAMPSIITE study.
The agency also committed to conducting an expedited review following resubmission, with labeling discussions expected to begin shortly thereafter. This regulatory alignment reflects the FDA’s continued commitment to advancing innovative therapies for patients suffering from serious rare diseases and highlights growing support for the accelerated approval pathway in areas where treatment options remain extremely limited.
One-Time Gene Therapy Targets Severe Neurological Disease
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Hunter syndrome (MPS II) is a rare inherited lysosomal storage disorder caused by a deficiency of the iduronate-2-sulfatase (I2S) enzyme, leading to the accumulation of toxic glycosaminoglycans throughout the body and central nervous system. The disease primarily affects boys and causes progressive neurological decline, developmental delays, organ dysfunction, and reduced life expectancy. Approximately 2,000 diagnosed patients worldwide live with MPS II, while more than 500 new cases are identified annually.
NAVSUNLI is designed as a one-time AAV-based gene therapy that delivers the IDS gene directly into the central nervous system, enabling long-term production of the missing enzyme beyond the blood-brain barrier. By addressing the underlying genetic cause of the disease, NAVSUNLI has the potential to provide durable therapeutic benefits and alter disease progression in a way that currently available treatments cannot achieve.
Transforming Rare Disease Treatment Through Gene Therapy Innovation
NAVSUNLI has already received several important regulatory designations, including Orphan Drug, Rare Pediatric Disease, Fast Track, and Regenerative Medicine Advanced Therapy (RMAT) status from the FDA, reflecting both the severity of Hunter syndrome and the therapy’s transformative potential. If approved, NAVSUNLI could not only become the first gene therapy for MPS II but may also qualify REGENXBIO for a Priority Review Voucher (PRV), creating additional strategic and financial value. Under a previously established partnership, Nippon Shinyaku’s U.S. subsidiary NS Pharma will commercialize the therapy in the United States following approval.
Company leadership emphasized that recent FDA interactions demonstrate a shared commitment to accelerating access to potentially life-changing therapies for rare disease patients. As REGENXBIO advances toward BLA resubmission, the program represents one of the most closely watched gene therapy opportunities in the rare disease sector and could establish a new standard of care for individuals living with Hunter syndrome.
Source: REGENXBIO press release
